This invention relates in general to an improved tip for a hollow, ultrasonically vibrated needle and more particularly to an improved tip for a phacoemulsification needle such as used in the surgical device shown by U.S. Pat. No. 3,589,363 issued June 29, 1971 to A. Banko and C. D. Kelman for a Material Removal Apparatus and Method Employing High Frequency Vibrations. The aforesaid patent describes an instrument for breaking apart and removing unwanted tissue and material, especially a cataract located in the anterior chamber of the eye, by ultrasonically fragmenting the cataract while simultaneously introducing fluid into the eye chamber and withdrawing the fluid and fragmented cataract particles. Briefly the device described includes a hand piece having an operative needle vibrating in ultrasonic range. The needle shaft is hollow and is in turn surrounded by a tubular sleeve. In operation the needle shaft including the surrounding tubular sleeve are inserted into the anterior chamber of the eye. Irrigation fluid is introduced through the hollow sleeve to provide a replacement for fluid withdrawn or lost from the eye chamber. The removal of fluid and suspended material from the anterior chamber is called aspiration and ideally there is no change in fluid content or anterior chamber pressure as a result of irrigation-aspiration.
It is highly desirable to emulsify the lens nucleus in situ because removing the nucleus from its original position and emulsifying it elsewhere in the eye creates a high probability of damage to other eye tissue, such as to the iris and corneal endothelium. However, commonly, the lens is not emulsified in situ because of the problems hereinbelow described, particularly the great danger of rupturing the posterior capsule.
Basically the eye is separated into two chambers, an anterior and posterior. These elastic, pressure-responsive chambers are separated by a thin, cellophane-like diaphragm called the posterior capsule located behind the lens. If the posterior capsule encounters a sharp instrument, particularly a vibrating needle, it is easily punctured and, once its structural integrity is broken, the posterior capsule generally splits and tears. The result is quite catastrophic. Vitrious humor is lost and lens particles and other material fall into the posterior chamber resulting in many complications, dangers, and difficulties.
The relative fluid pressures in the anterior and posterior chamber greatly influence the probability of posterior capsule rupture. Ideally the pressure in the anterior chamber should be slightly greater than the pressure in the posterior chamber. This keeps the posterior capsule bowed posterially and rigid. If the pressure in the anterior chamber becomes equal to or less than the pressure in the posterior chamber, the capsule provides a very infirm work surface and presents itself for damage. Control of both the macro pressure differential, i.e. the general overall pressures within the chambers, and the micro pressure differentials, i.e. the transient localized pressure differential particularly near the needle tip, are important. The problem of control of fluid content and pressure within the anterior chamber of the eye during irrigation-aspiration is discussed in U.S. Pat. No. 3,902,495 to S. N. Weiss and A. Broadwin for a Flow Control System. Various changes have been introduced into the conventional apparatus external to the eye to control pressure which have made contributions toward controlling the micro pressures. However, some problems cannot be controlled in this means or have not been fully controlled.
Pressure in the anterior chamber may be equal to or less than the pressure in the posterior chamber due to leakage exterior to the posterior capsule. Also local pressure transients occur at the needle tip, particularly because of a condition called "surge". As will be more fully explained later, surge is caused when the needle tip is temporarily occluded by lens material. A high vacuum quickly builds up in the needle lumen partially because of inertial flow and the occlusion is cleared. However, the high vacuum existing in the aspirating system and needle is then quickly transferred to the area immediately adjacent the needle tip and exerts a strong drawing power on adjacent tissues. If the posterior capsule is nearby, particularly if is floppy or bulging due to incorrect macro pressure differentials, it may easily contact the tip or another tool and be damaged.
It is of course desirable to make as few incisions and as small of incisions in the eye as possible while performing phacoemulsification. However, it is often necessary to physically manipulate the lens or other material. Present needle tips have a flat, angled face which is generally unsuited for these purposes. Therefore, another instrument such as an elongated spatula is used. Insertion of a manipulating spatula requires either a larger incision so that the manipulating tool can be inserted alongside of the needle; or withdrawal of the needle, insertion, use and extraction of the spatula and reinsertion of the needle; or another incision and use of the spatula in conjunction with the needle. A problem with the later technique, other than the extra incision, is the great difficulty in simultaneously coordinating two hand-held instruments while looking through a microscope.
Therefore, it is desirable to have an instrument capable of emulsifying the lens of an eye, which greatly reduces the probability of posterior capsule rupture, especially where the lens is kept in its original position.
It is also desirable to eliminate or greatly reduce surge and its concomitant hazards.
It is particularly desirable that such instruments and results be achieved by modification of that portion of the phacoemulsification apparatus inserted within the eye.
It is also desirable to have a phacoemulsification needle better capable of material manipulation.
It is also desirable to have an improved phacoemulsification needle tip better suited for sculpting.
It is even further desirable to have an improved phacoemulsification needle capable of lens emulsification and removal without the aid of another instrument.